There is a demand for estrogen-free contraception in order to reduce the risk of venous thromboembolism (VTE), particularly of obese women. A new long acting formulation of Levonorgestrel Butanoate (LB), delivered by injection, has been developed. Levonorgestrel (LNG) has a long history of clinical use in a variety of contraceptives (pills, intrauterine devices, and implants) and its efficacy and safety are well recognized. The proposed study in the NICHD Contraceptive Clinical Trials Network (CCTN) will be conducted in women of reproductive age in order to evaluate pharmacokinetics, the mechanisms of contraceptive efficacy, and safety of this new contraceptive. The enrolled subjects will receive a single injection of LB. The Recruitment will include enrollment of approximately 50% of subjects with BMI >=32kg/m2 but less than 40kg/m2. To evaluate hormones as defined in the protocol for the dose finding study for Levonorgestrel Butanoate (LB), Measurement of hormones as defined in the protocol will contribute to evaluation of the effects of the long-acting injectable formulation of LB.